The long term objective of this research plan is to define the molecular mechanisms which control globin gene expression in humans. Once these mechanisms are defined, new therapies for treatment of the many human hemoglobinopathies may be devised. The specific aim of this proposal is to define the nucleotide sequences which control the tissue specificity and developmental specificity of human globin gene expression. In order to identify these regulatory sequences, cloned human globin genes will be microinjected into the nuclei of fertilized mouse eggs and the expression of these genes examined in erythroid and non-erythroid tissues throughout development. If the injected genes contain all of the sequences required for correct tissue specific and developmental specific expression, globin mRNA and protein will be detected only in erythroid tissues at the proper developmental stage. Once animals which correctly express human genes are obtained, modified genes which are either constructed in vitro or isolated from patients with precisely defined hemoglobinopathies will be microinjected. Modifications which alter or abolish correct tissue specific or developmental specific expression will identify important regulatory sequences.